Conventionally, a memory of an image reproducing system such as a color scanner is composed of several line memories, each of which has a capacity corresponding to image data of one scanning line. Therefore, the capacity of the memory is regulated by the length (this word is defined in this specification as the length in the main scanning direction of an original picture (also limited by the circumference of an input drum) or by the length of a reproduction image (likewise limited by the circumference of a recording drum). However, usually only a portion of an original picture is desired to be reproduced, so the length of the portion is naturally shorter than that of the original picture. Actually, the length of the portion is a fraction of that of the original picture. Since any conventional image reproducing system stores all the image data of one scanning line of an original picture into a memory, the image data includes needless data.
FIG. 1(a) shows useless portions of an original picture I and its reproduction image II when the magnification ratio M is M.gtoreq.1. FIG. 1(a) shows the same when M&lt;1.
In FIGS. 1(a), (b), the length lp of the original picture I comprises the lengths of the portion to be reproduced and that of the useless portion. Image data of both portions are stored into a memory and read to be used for recording a reproduction image of length l.sub.R which also comprises the portions of lengthes l.sub.R1 and l.sub.R2.
Therefore the memory is compelled to deal with unwanted image data corresponding to the portion of length l.sub.p2 (of the input side) or l.sub.R2 (of the output side). Incidentally in FIGS. 1(a)(b), length l'.sub.p is the circumference of an original picture drum, and length l'.sub.R is the circumference of a recording drum when the magnification ratio M between both sides are M=1.
FIGS. 2(a)(b) show useless portions of original pictures I and their reproduction images II when (a) two or (b) four color separation images are recorded.
In this case, image data obtained by scanning the original pictures also comprises the image data corresponding to the portions of length l.sub.p2 /2 or l.sub.p2 /4 of the original pictures. In addition, there are provided spaces S between each of the color separation images.
Actually, useless image data corresponding to the spaces S are stored in the memory, they are invalidated by being masked when a reproduction image is recorded.
Consequently, the image data stored in the memory comprises the useless image data corresponding to the portion of length (l.sub.R2 /2)+S or (l.sub.R2 /4)+S.
Although FIGS. 2(a), (b) are based on a condition that the magnification ratio M is M&lt;1, the same thing can be said for a case M.gtoreq.1. In FIG. 1 and FIG. 2, the magnification ratio M is expressed by an equation M=l.sub.r /l.sub.p =l.sub.R1 /l.sub.p1.